Alex, those are great comparisons, amazing what the compression model does.
To a side topic I am still thinking about precision.
Half float is 16-bit, however there is one sign bit and 5 exponent bits which leaves 10 fraction bits. This can be thought of as using a 10-bit integer for differentiating the increments in a range of tonality which can be “floated” over an extended range of the 5-bit exponent. The “float” will allow for moving up and down a range, however the number of individual steps will remain the same. The precision remains fixed and at a level that I suspect might be too low when dealing with HDR ranges and for the discrimination of values important to the perception of textures.
For example I will present some practical observation from my photographic experiences.
I have an extensive background in Platinum/Palladium photographic printmaking as well as making what might now be termed analog negatives (optical/chemical film.) I also, for several years, explored making digital negatives (camera negative to digital scan to ink printed onto substrate) for this process. (The Pt/Pd process requires much UV light for exposure so printing required a contact negative (same size as resulting print.)
One thing I found from this exploration of Digital was that, whereas a gelatin silver print could be satisfactorily gleaned from a 10-bit digital ink-based negative, a Pt/Pd print would require at least 14-bits. I tried many ink printing techniques but could not successfully get a 14-bit ink printed digital negative. The Collotype Process comes very close (from examining such prints) but I did not have the means to pursue that.
Now why the 14-bit may be asked. That was what I determined necessary to deliver the character of the Pt/Pd print using a digital ink-based negative.
Pt/Pd prints have an inherent quality to discern very subtle changes in tone. Although not as white nor as black as a gelatin silver print, the Pt/Pd print will present many more increments of value between those limits. This is why a Pt/Pd print will deliver a much more tactile feel and perceived depth of the image, the qualities sought after from this process. (Of other photographic processes only the Carbon print can rival such qualities.)
I feel that delivering in HDR wide color can be, in a manner, like going from a gel-silver print to a Pt/Pd print, not in that the dynamic range has expanded (for with Pt/Pd it shrinks) but that there must be more steps/increments. This now presents double the problem as more bit depth will be needed for the larger dynamic range and more bit depth will be needed to provide for more increments of tone.
Another place where an increase in incremental tone values is desired is in the lower (darker) tones. Even though these extra increments may not be readily apparent VFX has shown advantage of having them as I surmise the apparent tactile quality will as well.
10-bit depth is not enough for HDR. And it will fail further when more steps are needed to provide for the subtle texture quality as well as providing for more increments in the lower tones.
Tactile quality (or micro texture) is valuable in helping draw one into and keep involved in the story. And not only that, it can help manipulate one’s feelings and perception. An orange must have the appropriate amount of tactile quality to feel like an orange. Skin must have appropriate tactile quality to appear alive. Film has been able to provide enough, digital can but, in the current circumstances, is being held back by limited precision. If tactile quality and texture are not of importance then why did ARRI go to the effort to make such an improvement in their last camera.
Please keep in mind that texture and tactile quality are not just contrast. They rely on subtle discrimination of tonal and color values.
Another field where this tactile quality is appreciated is medical imaging where 16-bit look up tables and calculations are utilized.
And another analogous example would be when having to move from 8-bit to 10-bit to cover P-3.
10-bit is just not enough for HDR. So whether 12, 14, 16 bit or even 11, half float is not going to be enough. Unfortunately this means that significantly more resources (hardware, energy and time) will be necessary. Calculations will just need a bit more precision (pun intended.) And although much of tactile quality concerns could be topics for ACES 3.0, it seems necessary that the calculations for now (ACES 2.0) should be of a higher precision.
It might be a good test to run the models with float32 and determine if there are notable fine increments worth preserving and also if any issues with rounding errors or whatever then become solved.
